This invention relates to a thermostatic heater device for liquids, in particular for the water of aquariums.
Heater devices with temperature control for liquids, in particular for the water of aquariums, are known. One of these is described in U.S. Pat. No. 5,750,960 and comprises a dielectric film on which there is printed a resistive element electrically powered via a thermostat.
This dielectric film is housed within an annular interspace bounded by two cylindrical walls, the inner of which is constructed of glass and through the interior of which the liquid to be heated passes. One portion of the annular interspace has a greater width to define a chamber housing the thermostat, which is provided with a heat-sensitive element facing the heating element in such a manner as to determine its temperature and hence, indirectly, the temperature of the water circulating through the device.
This known heater device has proved well suited in particular to maintaining the water of an aquarium at the desired temperature, but at the same time has highlighted some aspects which could be improved.
One of these is that the heating element is in direct contact with the glass of the inner cylindrical wall, and hence does not posses the characteristic of double electrical insulation, as currently prescribed for all non-earthed electrical appliances not powered at low voltage. In this respect, the provision of double insulation poses constructional problems which up to the present time have not been satisfactorily solved.
A further improvable aspect is that in that particular device the heat-sensitive element is positioned to the side of the heating element, not in contact with the cylindrical glass wall. Because of this the sensitivity of the regulation is influenced by the temperature not only of the water, ie the quantity effectively to be controlled, but also of the heating element.
An object of the invention is to provide a thermostatic heater device in which, in contrast to known devices, those parts under voltage are provided with double insulation, so satisfying current regulations.
A further object of the invention is to provide a thermostatic heater device which is of extremely simple production and safe and reliable operation, even if abnormal situations arise.
These and further objects are attained according to the invention through a thermostatic heater device as claimed in claim 1.